1. Field of the Invention
The present invention relates to a signal separator and, more particularly, to a Y/C separator having a function of subsampling a digital composite video signal.
2. Description of the Related Art
In the existing color television broadcast system, a composite video signal obtained by superposing a color difference signal (to be referred to as a C signal hereinafter) which is balance-modulated by a chrominance subcarrier on a luminance signal (to be referred to as a Y signal hereinafter) is used as a television signal to be transmitted. For this reason, a reception side requires a luminance/chrominance (to be referred to as Y/C hereinafter) separator in order to reproduce the Y signal and C signal. A low-pass filter or band-pass filter is used as a conventional Y/C separator. However, the low-pass filter or band-pass filter cannot perform perfect Y/C separation, and cross color or dot interference occurs, thus degrading image quality. A comb filter was developed later to improve Y/C separation performance. However, when the comb filter is used, the Y/C separation performance is improved but resolution in a diagonal direction of the screen is degraded.
In order to solve this problem, in particular, in order to achieve high image quality, a so-called motion adaptive Y/C separator used in a digital video system which has a digital circuit corresponding to a video detector and the subsequent circuit has been developed. The motion adaptive Y/C separator changes a parameter in accordance with a pattern to perform Y/C separation corresponding to motion of an image, and is described in an article entitled "A Motion Adaptive High-Definition Converter for NTSC Color TV Signals", SMPTE journal, May 1984. In this acticle, since a calculation is not performed in the horizontal and vertical directions of an image as long as the image is a still image, efficient Y/C separation free from degradation of an image can be achieved.
However, the conventional adaptive Y/C separator requires delaying a composite video signal by one frame period. Therefore, a circuit scale must be increased accordingly.
For this reason, a demand has arisen for a Y/C separator which keeps a performance equivalent to the conventional Y/C separation performance, and can reduce a memory capacity as much as possible.